In the past to make use of the anti-oxidant anti-corrosion properties in only hydrocarbons imparted by Ca salicylaldimine ##STR1## wherein R is alkyl, an aminoethyl (H.sub.2 N.sub.2 -CH.sub.2 CH.sub.2 -), hydroxyethyl (HO-CH.sub.2 CH.sub.2 -) or thiolethylene (HS-CH.sub.2,CH.sub.2 -), it has been necessary to prepare a derivative of the salicylaldimine which would make it soluble in oily hydrocarbons such as distillate fuels (gasoline, diesel fuel, heating oil, etc.) and lubricant oils. For example, according to U.S. Pat. No. 3,296,130 a salicylaldimine where R is CH.sub.2 CH.sub.2 CH.sub.2 -NH.sub.2 is reacted with an oil-soluble aklenyl-substituted succinic acid (alkenyl-substituent was tetrapropenyl).
The same oxidation and/or corrosion inhibition of an salicylaldimine could be made available providing solubility in oily hydrocarbons could be imparted to salicylaldehyde from which the imines were derived by the known Schiff Reaction between an aldehyde and an amine. To impart such solubility in an oily hydrocarbon it would be necessary to substitute one of the ring carbons an alkyl-substituent having at least six carbon atoms. However, alkylation of the salicyl moiety by conventional means is sufficiently difficult to make it commercially unattractive. It is known that an oil soluble salicylic acid can be prepared through a modified Kolbe reaction wherein a solution of a sodium phenate salt of a C.sub.6 or higher alkyl-substituted phenol is reacted with carbon dioxide.
However, our search of the prior art did not bring to light any alkylation of salicylaldehyde or reaction of an alkyl-substituted phenol for the preparation of a commercially feasible route to an alkyl-substituted salicylaldehyde which would be soluble in an oily hydrocarbon such as the distillate fuels and lubricant oils.
We have found a rather simple and commercially feasible route for the preparation of an alkyl-substituted salicylaldehyde which will be soluble in said oily hydrocarbons.